The word 'unwelcome' is a transparent english formation built from the native germanic adjective 'welcome' and the common negating prefix 'un-'. The core 'welcome' itself originates from old english wilcuma, a compound of wil- (pleasure, desire) and cuma (guest, comer), literally meaning "a desirable guest." The prefix 'un-', with its ancient proto-germanic root un-, has consistently functioned to express negation or reversal. Therefore, the logic of 'unwelcome' is direct and compositional: it describes something or someone that is the opposite of being received with pleasure or desire, effectively meaning "not received gladly." This straightforward morphological process showcases the analytic nature of english in creating antonyms through prefixation.

Structure: un (not) + welcome (greeted with pleasure) - un: a prefix of germanic origin (old english) meaning "not," serving a negating function. - welcome: from old english wilcuma, meaning "a person whose coming is pleasing," functioning as the core adjective.